In the art, e.g. as marketed by the present applicant, offshore drilling vessels are known that comprise:
a floating hull subjected to heave motion, the hull comprising a moonpool,
a drilling tower at or near the moonpool,
a tubular string hoisting device, the tubular string for example being a drill string,
hoisting device comprising:                a main hoisting winch and main cable connected to said winch,        a crown block and a travelling block suspended from said crown block in a multiple fall arrangement of said main cable, which travelling block is adapted to suspend a tubular sting, e.g. a drill string, therefrom along a firing line, e.g., with an intermediate topdrive adapted to provide a rotary drive for a drill string,        
a heave compensation system adapted to provide heave compensation of the travelling block, the heave compensation system comprising a main cable heave compensation sheave in the path between said main hoisting winch and the travelling block, a passive and/or active heave motion compensator device connected to said main cable heave compensation cable sheave,
a riser tensioning system adapted to connect to a riser extending along the firing line between the subsea wellbore and the vessel, the riser tensioning system comprising a tension ring and tensioner members connected to said tension ring.
In a known embodiment, e.g. as disclosed in U.S. Pat. No. 6,595,494, a travelling block heave compensation system comprises two main cable heave compensation sheaves, each one in the path between one of the said main hoisting winches and the travelling block. Each of these sheaves is mounted on the rod of a compensator cylinder, with these cylinder connected, possibly via an intermediate hydraulic/gas separator cylinder, to a gas buffer as is known in the art.
In the offshore drilling field it is also known to make use of a slip joint, also referred to as telescopic joint. Commonly the slip joint has a lower outer slip joint barrel and an upper inner slip joint barrel, wherein the lower outer barrel is adapted to be connected to a fixed length section of the riser extending to the subsea wellbore to the riser. In known embodiments the slip joint is provided with a locking mechanism, e.g. with hydraulically activated dogs, which is adapted to lock the slip joint in a collapsed position. Known slip joints provided a higher pressure rating in the collapsed and locked position than in the dynamic stroking mode. For example slip joints are known to have one or more metal-to-metal high pressure seals that are operative in the collapsed and locked position, whereas in dynamic mode a hydraulically activated low pressure seal or seals are operative.
In the offshore drilling field it is known for the tension ring of the riser tensioning system to be connected to the outer barrel of the slip joint. Known tensioning systems include a wireline tensioning systems, wherein wire lines extend from the tensioning ring to tensioners on-board the vessel. Also known are direct-acting riser tensioning systems, wherein multiple cylinder units directly engage on the tension ring.
WO2010/071444 discloses a floating arrangement with a riser tensioning system. The riser tensioning system is provided to maintain an approximately constant tension in the riser when the floating arrangement moves in the water. The tensioning system is here indicated as a first set of heave compensating devices. The floating arrangement further comprises a work deck which is arranged in an opening in a drill floor. The work deck can move relative to the drill floor by a second set of heave-compensating devices to keep the work deck at an approximately constant distance from the seabed.
In the field of drilling so-called closed circulation methods become increasingly attractive, e.g. in view of improved control of pressure within the wellbore, e.g. during drilling. To this end a rotating control device, RCD, is arranged, commonly above the slip joint, to closed of the annulus between an upper riser section and the tubular string extending through the riser. One or more flowhead members below the RCD, or integrated therewith, allow for connection of one or more hoses so that annular fluid flow, e.g. return mud, can be transferred to the vessel. Due to the sealing of the annulus by the RCD control of fluid pressure in the annulus is possible, e.g. in view of techniques such as Managed Pressure Drilling.